Voltage booster

[AbyssUnderground]

Hello,

Ive been looking for a while for something suitable for my problem but can't seem to find anywhere that does what I want so I decided to ask  here.

Im using a 1.5w trickle charge panel but its enough to keep the battery topped up as its used for lighting only when camping for 2-3 hours a night in the summer.

My problem is that the panel rarely gives out over 10v due to low light and rarely any sun (in the UK). Because of this the battery will not charge. I need some circuitry that will boost the voltage up to 13.5v or more so the battery will charge in nearly all light conditions. It doesnt matter about low current as long as it gets some charge into it.

Ive asked a friend to design this but he seems to be putting it off to much and we're not getting anywhere with it. I was wondering if anyone here had any design plans for such circuitry that I could use and build myself. It needs to be as low cost as possible.

Thanks in advance,

Andy.

[Flux]

Andy to be honest I suspect that with a panel as small as that there will be so little power available in low light that even if you manage to boost the voltage there will be nothing useful. Even big panels are little use in low light.

Flux

[AbyssUnderground]

Thanks for the reply. I did fear this. The problem is Im going camping for 10 days and I want to get into this whole "green power" business so I thought it would be a good idea to get things going like this. I wanted to try not using anything but solar to charge this battery up for the 10 day trip.

Would buying a bigger panel and using this booster device help? I mean more current at lower voltages means a little less at higher but still more compared with a smaller panel?

[wiredwrong]

You might try something like this, http://Http://www.tunecharger.com, I have a panel that is about the same size as yours and I think Im going to try it myself if time ever permits, I think I read about this here on Fieldlines first you may try a search of this board and see what was said about it. He gives the plans away on a Yahoo Group, I'd be sure to set your prefrences to no email if you join it.  

[Flux]

A bigger panel will help if you have room. It would be better to have a panel with higher open circuit volts rather than try to boost. You are not likely to get better than 90% efficiency from a small booster and 80% is more reasonable. most nominal 12v panels give 15v in light levels that make little power, it is normally current rather than volts that increases with light. If your panel was cheap it may be worth trying 2 in series in poor weather. you could connect them in parallel on good days.

Flux

[BT Humble]

Here you go, I knew I'd saved this link for a reason:

http://www.talkingelectronics.com/Projects/SolarCharger/SolarCharger.html

BTH

[oztules]

If you only have feeble power to feed a booster, chances are that the booster will eat up a significant proportion, before you look like overcoming the battery internal emf.

You cant boost the power, only the voltage at the cost of power.

The only thing you do get for free is the sunlight itself, so  i'd follow flux's advice  and get another cell, and put it in series, at least you have double whatever resource you had, and have introduced no losses. you have to be in front of your current position. converter will probably just compound the problem, ie more losses out of an already stressed system.

.......oztules

[RP]

Try this instead (without the trailing comma)

http://www.tunecharger.com

[ghurd]

The 10V figure, is that while connected to the battery?

If so, the panel is doing all it can and working properly, it is just very tiny. 2 in series won't help. 2 in parallel would help, a little bit.

If the 10V is while not connected to anything, it is a 6V panel. 2 in series will make it do some charging.

There is no mention of the light being used 2-3 hours a night. Anything more than a few LEDs and that panel can not keep up anyway.

G-

[AbyssUnderground]

Thanks for all the replies. Ill get round to looking at the links soon.

Im going to be using a cold cathode tube that uses around half an amp but is very bright. You can see how im hooking it up on a web page I recently made and am still working on: http://m3ezw.no-ip.com/stuff (while the link works).

The panel is giving out 10v open circuit in low light but I know for a fact its not 6v because it says on the box 12v and Ive seen 21v open circuit on a very sunny day. I paid £20 for this cell so it is pretty cheap. I think the blue flashing LED to say its working takes up half the power at least (well, maybe not, but the led is pointless as far as im concerned).

As you say it might be worth getting 2 panels and hooking them up in series on bad days and parallel on good days. I think the shop I got it from still sells them.

Ill take a look at the links given and see what other options are. Keep the ideas and comments coming :-)

Cheers for the help so far.

[ghurd]

Bad news.  

With 2 to 3 hours at 1/2 amp is ~1.25ah. A 1.5W 12V PV is about 90ma peak. For a solar insolation of 5 hours, the light will run less than 1/2 hour per day from the PV. Not including any losses.

That LED is using 20ma. Such a waste on a small PV.

Maybe run down to the VW dealership and ask if they have a couple 'extra' solar panels.  Those have a lot higher cell count so they will (sort of) work better in low sun, and though rated at 175ma mine all go past 200ma into a battery. They also have a charge controller, at least many of the new ones.

And they can be free if you ask right.  

G-

[AbyssUnderground]

Is there any way to remove the stupid LED? Could I drill the hell out of the top of it or will that cause it to short? I need all the power I can get here.

The panel is rated at a top current of 125mA at top capacity. I know it wont provide enough power to keep it charged up, but at least it will provide some power to keep a charge in the battery.

I took a look at the links provided. I cant read french to that was no use, but the second one I was interested in. I sent it to my techy friend who said he will take a look at it for me and possibly build it if he can get the components for me.

I dont know of any VW dealerships around my area so that idea is also out of the window. Ill have to find another £20 and get another panel I think. :-(

[ghurd]

Open the part with the LED, cut the LED off. That should deactivate the circuit. I think.

VW PVs. Check Ebay.  If your 'funny L' is ~= to US$2, one should cost 'funny L' 15. Including shipping. Might take a week or 2 or 3 (ebay is strange to me) to get them for that price.  Not sure I ever paid over US$20 total each, in quantity(6-20).

My Chinese keyboard here in the US has no English pound or euro key.

Did you see my post about this kind of thing...

http://www.fieldlines.com/story/2005/8/21/205627/022

Maybe you will get a new idea.

[AbyssUnderground]

£1 is roughly $1.70 :-)

[AbyssUnderground]

I've managed to get my friend to build a circuit to boost the voltage. He said it will be about 85% or higher efficient and wont take more than 20mA out of the solar panels power. He is making it so the voltage will always be 14.5v, even if the voltage is higher. He says this way the battery will get a better charge.

Its currently sunny here and the solar panel is maxing out at 21v open circuit.

[AbyssUnderground]

I've decided I should go with another panel. Does anyone know where I can get at least a 5w panel but not from ebay? Ive looked for these vw pv's but there weren't any on when I looked.

maplin.co.uk is the only site Ive found but they only have 1.5w panels for £20. Ive probably got a top budget of £30 at most.

[ghurd]

They have a VW PV in London right now for GBP 14.99. Item #4614547469

A 'buy now' in Kent for GBP25. Item #4601158587

All mine test out in real life past 3.8W.

[AbyssUnderground]

I just looked at that item but it ended 2 days ago, unfortunately.

I also just visited maplin and found they had a 1.5w solar panel on offer at £9.99 so I bought one. Its identical to the one I already have so they will be a good match.